Private Land Mobile Radio Service (PLMRS) is widely used by private user groups such as businesses and public service organizations for general-use portable operations such as dispatch, coordination and emergency radio communications. Corporations frequently utilize these systems for on-premises and campus activity coordination such as allowing building maintenance, security or medical teams to remain in communication during normal or extraordinary circumstances. Radios are usually hand-held units and are frequently attached to the user's belt via a holster. Some applications, such as shipping area electric-carts, hi-lift inventory management, or golf cart-like electric personnel movers, are fitted with dash-mounted units.
The essence of PLMRS is non-duplexed (simplex) spectrum usage for voice communication. That is, the same frequency channel is used for both directions of conversation, with a push-button switch being used to key the transmitter when an individual wishes to call another unit or respond conversationally. Additionally, all users of a common group in a PLMRS system share the same frequency channel.
Wireless LANs (WLANs), such as the IEEE 802.11 standard, are becoming popular in business environments as a means of allowing exchange of computer data between laptops and wired LAN systems. Such systems usually operate, like PLMRS, with both directions of transmission sharing the same radio resource, but communicate only non-time-bound data.
Recently, the rise of multimedia content on the Internet has provoked a desire for wireless LAN systems to provide support of time-bound packet streams in addition to asynchronous data bursts. Such streams may contain a variety of content such as audio, video, and telephony. In response to the need to support streaming operation, wireless (and wired) LAN-like transmission systems have recently moved toward adoption of protocols which provide Quality of Service (QoS). These protocols provide the ability to allocate portions of the WLAN radio resource (throughput) to individual streams. The protocols usually employ a form of packet reservation via scheduling to minimize delay and contention during transmission of the streaming data so as to provide a guaranteed level of QoS.
Further, as a result of the development of QoS protocols, for example “MediaPlex” an invention of AT&T Labs, it has become possible to provide voice telephony via wireless LANs. Voice telephony over wired LAN facilities, cable, DSL, and other broadband packet transmission systems is accomplished by a number of protocols such as H323, media gateway control protocol (MGCP), session initiation protocol (SIP), etc. The protocols are intended to provide full-duplex telephony over time-segmented, shared resource systems.
The present application is related to U.S. Pat. No. 6,862,270, entitled “An Architectural Reference Model for QoS-Driven Wireless LANs”, invented by J. M. Ho, and issued Mar. 1, 2005; to U.S. Pat. No. 7,031,287, entitled “Centralized Contention and Reservation Request for QoS-Driven Wireless LANs” issued Apr. 18, 2006 and to U.S. Pat. No. 6,804,222, entitled “An In-Band QoS Signaling Reference Model for QoS-Driven Wireless LANs”, invented by W. Lin and J.-M. Ho, and issued Oct. 12, 2004; to U.S. Pat. No. 7,151,762, entitled “Virtual Streams for QoS-Driven Wireless LANs”, invented by J.-M. Ho and W. Lin, and issued Dec. 19, 2006; to U.S. Pat. No. 6,970,422, entitled “Admission Control for QoS-Driven Wireless LANs”, invented by W. Lin and J.-M. Ho, and issued Nov. 29, 2005; to application Ser. No. 09/616,896, entitled “Frame Classification for QoS-Driven Wireless LANs”, invented by J.-M. Ho and W. Lin, and filed Jul. 14, 2000; to U.S. Pat. No. 6,850,981, entitled “Frame Scheduling for QoS-Driven Wireless LANs”, invented by J.-M. Ho and W. Lin, and issued Feb. 1, 2005; and to U.S. Pat. No. 6,999,442, entitled “RSVP/SBM Based Down-Stream Session Setup, Modification, and Teardown for QoS-Driven Wireless LANs”, invented by J.-M. Ho and W. Lin, and issued Feb. 14, 2006; to U.S. Pat. No. 7,068,632, entitled “RSVP/SBM Based Up-Stream Session Setup, Modification, and Teardown for QoS-Driven Wireless LANs”, invented by J.-M. Ho and W. Lin, and issued Jun. 27, 2006; and to U.S. Pat. No. 6,950,397, entitled “RSVP/SBM Based Side-Stream Session Setup, Modification, and Teardown for QoS-Driven Wireless LANs”, invented by J.-M. Ho and W. Lin, and issued Sep. 2, 2005; and to U.S. Pat. No. 7,068,633, entitled “Enhanced Channel Access Mechanisms for QoS-Driven Wireless LANs”, invented by J. M. Ho and W. Lin, and issued Jun. 27, 2006; and to U.S. Pat. No. 7,031,287, entitled “Centralized Contention And Reservation Request For QoS-Driven Wireless LANs”, invented by J-M Ho et al., and issued Apr. 18, 2006; and to U.S. Pat. No. 7,039,032, entitled “Multipoll for QoS-Driven Wireless LANs”, invented by J.-M. Ho and W. Lin, and issued May 2, 2006; each of which is incorporated by reference herein as to their entire contents. The present application is also related to U.S. Pat. No. 7,002,995, entitled “Broadband Network With Enterprise Wireless Communication System For Residential And Business Environment”, issued Feb. 21, 2006 and U.S. Pat. No. 7,010,002, entitled “Broadband Network With Enterprise Wireless Communication Method For Residential And Business Environment” issued Mar. 7, 2006, each of which is incorporated herein by reference as to their entire contents.
Voice-over-IP (VoIP) systems using these protocols are beginning to appear as an alternative to conventional circuit-switched telephone networks such as PBX and Centrex. Using new QoS-enabled wireless LANs, it is possible to extend VoIP telephony via IEEE 802.11-like transmission systems to provide mobility. Using the new VoIP capability, businesses may utilize a combination of LAN and wireless LAN resources to augment or replace embedded circuit-switched telephony systems. Over the next decade, such replacements are anticipated to accelerate rapidly, due to a desire to minimize information technology (IT) expenditures by consigning all traffic to a single, unified transmission system. An advantage of wireless LANs with QoS is the ability to support phased migration to an all-LAN architecture by eliminating the need to rapidly convert all conventional phones to VoIP. Such a phased approach minimizes retraining of personnel as well as disturbance of operations during a cut-over.
The combination of computers and telephones also provides simplified user migration from conventional phones to VoIP with the use of the high-resolution touch-screen display. PDA-like instruments with high-resolution displays and touch screens are becoming more sophisticated and inexpensive and afford the opportunity to create an “image” of the keypad of the legacy phone on the new VoIP phone. Then, using a “soft” PBX or switch with appropriate software, it is possible to make the PDA emulate the particular legacy instrument with which users have developed comfort.